Real cases

Two of the ideas you practise, meeting in one real situation. Choose, see what actually happens, then reflect.

A case · you decide

Trice & Baton — a 17-year-old debugging a like-counter in a club project

The idea in play: counter += 1 is three steps (read, add, write), and the order the tasks run in can lose one update.

Two tasks each run counter += 1 once, starting from 0. Sometimes the counter ends at 2, and sometimes at 1.

Trice: each += is read, add, then write.

Baton: the two tasks' reads and writes can interleave in any order.

What is the smallest final value possible?

“In reality, every technology reflects decisions made by designers, companies, and communities, and carries the values and power of those choices.”

A case · you decide

Isla & Sheara — a 16-year-old choosing a fix for the same race

The idea in play: shared, mutable state is where races live; an actor serialises access so only one task touches it at a time.

The counter is shared between two tasks and both change it. Isla's teammates suggest three fixes.

Sheara names the problem: the state is shared AND mutable.

Isla's tool is the actor: whatever lives inside it is touched by one task at a time, each change finishing before the next starts.

Which fix is correct?

“In reality, every technology reflects decisions made by designers, companies, and communities, and carries the values and power of those choices.”